Apparatus for cellulose processing



April 8, 1952 w. H. BRADSHAW ETAL APPARATUS FOR CELLULOSE PROCESSINGOriginal Filed Oct. 27, 1942 BY C.

IN V EN TORS William 11.5mm:law/a William R. Sc/zmitqdk ATTORNEYPatented Apr. 8, 1952 APPARATUS FOR CELLULOSE PROCESSING William H.Bradshaw, New Rochelle, N. Y., and

William R. Schmitz, Jr., Newark, N. J., assignors to E. I. du Pont deNemours & Company, Wilmington, Del., a corporation of Delaware Originalapplication October 27, 1942, Serial No.

463,514. Divided and this application December 6, 1947, Serial No.790,164. In Argentina April 20, 1943 the preparation, in a continuousmanner, of alkali cellulose of uniform composition, which al-' kalicellulose is eminently suited for conversion into a cellulosederivative, such as sodium cellulose xanthate for use in the viscoseprocess.

This application is a division of our copending application Serial No.463,514, flled October 27, 1942, now Patent No. 2,452,542.

In U. S. 2,392,269 to W. R. Schmitz, Jr., flied September 10, 1943, andissued January 1, 1946, there is described an apparatus which utilizes adevice for supplying heat to a slurry of alkali cellulose, the devicebeing actuated by means which are dependent upon changes in theviscosity of the slurry. In that apparatus an increase in alkalicellulose content of the slurry produces a pressure drop at a pressureactuated viscosimeter, which in turn causes the slurry to be heated to ahigher temperature. The increased temperature of the slurry results in adecrease in the viscosity of the slurry and this causes the viscosimeterto be returned to the non-operating condition. The uniform compositionof alkali cellulose is thus controlled. Such heating and actuating meansare not used in the present invention.

Although many attempts have been made to produce alkali cellulose in acontinuous manner, such processes did not permit a sufliciently accuratecontrol to produce alkali cellulose of 4 Claims. (Cl. 23-260) uniformcomposition. Previous to this invention, the generally accepted methodof producing alkali cellulose included the steps of steeping pressedsheets of cellulose, prepared from wood pulp or cotton linters, in anaqueous sodium hydroxide solution in a steeping press.

The excess sodium hydroxide solution was then pressed from the steepedsheets, and the latter subsequently comminuted to the desired size.

It is an object of this invention to provide an improved apparatus forthe continuous pro- ;iuction of alkali cellulose of uniform composiion.

Other objects of the invention will appear hereinafter.

The objects of this invention may be accomplished, in general, bycontinuously feeding cellulose into a slurry-forming receptacle, thefeeding of cellulose being unavoidably subject to slight fluctuations infeeding rate, continuously adding sodium hydroxide solution to saidreceptacle at a substantially constant rate, withdraw ing the slurryfrom the receptacle at a constant volume rate of slurry but with slightfluctuations of alkali cellulose content in the slurry, and continuouslyremoving the alkali cellulose from the slurry at a constant volume rateof alkali cellulose, while permitting increase or decrease of the massof slurry passing between the point where it is withdrawn from thereceptacle and the point where the alkali cellulose is separated fromthe slurry.

The details of the present invention will be more clearly apparent byreference to the following detailed description when taken in connectionwith the accompanying illustration, in which:

The figure is a diagrammatic side elevational view, with parts shown insection, of an apparatus suitable for use in accordance with theinvention.

Referring to the drawing, reference numeral l0 designates aslurry-forming receptacle which is preferably provided with atemperature controlling jacket 8 and jacket inlet and outlet means H andI3 respectively. The jacket inlet means H may be provided with athrottling valve l5 controlled by a thermostatic temperature control H.The receptacle l0 contains a cellulose feed inlet l2 and a sodiumhydroxide solution inlet means [4. The inlet means I 4 is connected to aconstant level supply means [6 comprising a supply conduit ill for thesodium hydroxide solution and an overflow conduit 20. By this means,sufficient solution will flow into the receptacle [0 to maintain theslurry therein at a constant level. The receptacle I0 is provided with adraft tube 22 in which is positioned a rotatable shaft 24. The shaft 24,which may be rotated by means of motor 26, contains a plurality ofstirring and cellulose disintegrating blades 28. The blades 28 cooperatewith bars or blades on the internal periphery of the draft tube 22 totear and disintegrate the cellulose material and force the resultingslurry of alkali cellulose through the bottom of the draft tube 22. Aportion of the slurry will pass upwardly between the tube 22 andreceptacle [0 to be again forced down through the draft tube. Anotherportion of the slurry will be drawn through slurry outlet 30 by means ofcentrifugal pump 32. An agitating device 3| may, if necessary, bepositioned between outlet 30 and pump 32. The agitating device 3| willdisintegrate any remaining pieces of cellulose substantially into itsfibrous state and thoroughly mix the same into the slurry. If desired,the device 3| may be provided with a screen, having for example a A;inch mesh, to insure the formation of a substantially fibrous slurrymass.

Thepump 32 passes a minorportion of the slurry ,to metering .device 34and. aimajor portion of the slurry through conduit 36 back to the top ofthe receptacle l0. positioned on the end of conduit 36 so as to pass theslurry into the receptacle with .considerable force. Any sheets ofcellulose passing under nozzle 31 will thereby beforced into draft tube22 to be disintegratedtherein.

The metering device 34 may consistof a constant volume gear pump and isconnected to a fluctuating volume slurry receiver 38. -A conduit 39connects the bottomo'f receiver-38 .tora slurry separating container 49.The container 40 is provided with slurry separating rolls 42 and 44which are adapted to press the :islurry forced in contact therewith toseparate the solid :alkalL-cellulose from the sodium :hydroxide -:solu-*tion. The'slurry separating container 40 is.pref- -erably constructedin the 'manner "described in therzcopending patent application ofWilliam .R. Schmitz, Jr., Serial No. 338,443, filed June 1, 1940 (now.Patent No. 2,308,031, issued January 112, 51943) The slurrypressrolls42 andz44 are sealed in-.thecontainer-JU to permit the slurryin the icontainer tobe maintained under pressure. .The slurry pressrolls when rotating at a givenperripheralgspeedwill passasubstantiallyconstant --volume of the solid alkali cellulose1pernnit oftime.regardlessmflslightfluctuations in; the alkali 'cellulose:contenttof theislu-rry. 'With the alkali cellulose being fed to thepress rolls 42 find .atcazsubstantiallynonstant:rate-the pressed; alkalicellulose 46 willtcontain a substantially constant percentagebfasodiumhydroxide solution.

The above described device will operate sub- :stantially as follows:

Cut sheets 9 of cellulose, ;or-.anyother :desired form of .cellulose,rareffed -to the slurry-forming receptacle Illyata feeding ratemaintained as uniform :and constant as-possible. This may, :forrexample, be vdone 'by feeding the-sheets 'by-hand or .iayifeedingapparatus of the itype describedain .schmitz :Patent No. 2,253,140. Such:feeding of 'celluloseris, however, always subject to slight fluc-"tuationsinifeedingirate,as will appear later herein. :Sodium hydroxideis passed intothe recep- A nozzle 311s tacle flfl-zby means -.of-aconstant level supply device Ii. By means of :such :a device, sufficientsodium :hydroxide is constantly added to the 'slnrryeforming receptacleto maintain the level .of theslurry in the latter substantiallyconstant. As.;the ,cellulose is fed .into the receptacle, it --is,gguided'into the draft tube 22 in which the cellux1059 will bedrawn bymeans ofithecomminuting blades-28, which are rotated byzmeans :of (motor.2Beand-shaft 2-4. Thecellulose will be torn and .-1disintegrated andthoroughly mixed with the sodium hydroxide solution to form .a fibrous-slurry massof alkalicellulose. A portion .of the :ZSIHHY-Millib passedfrom the .bottomof the draft ..tube;.upwards.between the draft tube andthe :receptacle .to againz'fiow through therdraftitube. Anotherportionof the slurry, will be ,drawnfrom ethebutlet 3.0 of the receptacle bymeans ofcen- -trif-ugal .pump .32. A portion of this withdrawn slurry ispassedto a constant volume :n'leterin-g .device 34 and :a major portionofthe slurry is passed into conduit 36 to be recirculated throughthemeceptacle Ill. The conduit 36 is provided withanozzle 31 positionedabove the draft tube 22 .toforce .the. recirculated slurry into thereceptacle with sufficient force to press cellulose contained in the topof the receptacle down into the draft tube to be disintegrated therein.Preferably, a heating or cooling ,fluid is passed through jacket 8 tomaintain the temperature of the slurry constant. The quantity of fluidpassed through the jacket is automatically regulated by throttling valvel5 and thermostatic control H.

The constant volume metering device 34 passes a constant volume ofslurry per unit of time into a. fluctuating volume container 38.Although the volume .of. slurry passed per unit of time by the meteringdevice will be constant, the alkali cellulose content of the slurry willfluctuate due to'the above-mentioned fluctuations in the feeding rate ofthe. cellulose into the receptacle. The slurry mass forwarded by themetering device 34 flows through fluctuating volume container 38 andinto a slurry separating container 40. The

:slurry .ispassedinto the container 49 under a .certain amount ofpressure, preferably of the .order.of.10 to 20 poundsper square inch.The slurry in the container 40 will be forced against 25.

rotatingslurry press rolls 42 and 44, thereby depositing .a. mat ofalkalicellulose on the rolls and filteringliquid caustic therefrom. Uponrotation,..the press .rolls willpress the remaining liquid sodiumhydroxide from the solid alkali cellulose to ..the desired alkalicellulose to liquid caustic ratio. .The. slurry press .rolls 42 and 44are sealeddnthe --,container 40 to permit the slurrycontained therein tobe, maintained under .the .abovementioned pressure. .The .slurry press:rolls are substantially non-yielding relative to each other andtherefore, whenrotating ,ata con- .stant. speed, pass .-a substantiallyconstant, uni- ,form olume of alkali cellulose per unit. of time,regardless ;of the fluctuating content of alkali cellulose ,in theslurry. As the alkali cellulose .content of the-slurry is slightlyincreased, the

thickness of thedepositedmat of alkali cellulose on .thepress rolls isincreased, thereby slowing .downtheflltration therefrom of liquidcaustic.

As aresult, there-will be an increase in the total slurry volume betweenthe metering device-34 and themes, rolls 42 and. This additional volumeis.,.temporarily stored in the fluctuating volume receiver 38 with anaccompanying increase in pressure therein. As nthealkali cellulosecontent ,of. the slurry is subsequently decreased, the stored amount ofslurry in the receiver 38 is gradually forwarded to the. container .40,thus compensating ,for fluctuations .in alkalicellulose content of the.slurry and in turn compensating for fluctuations in the feedin g.rate ofthe cellulose.

-.As above repeatedly stated, it is practicably ,irnpossibleto feed thecellulose to the receptacle at,a.constant, rate of feed since cellulosesheets contain. slight ,non-unlformities in weight of cellulose.Furthermore, such sheets of cellulose frequently vary in the moisturecontent therein.

.For ,this reason, it has been exceedingly difficult .heretofore :to,pro.duce.alkali cellulose of uniform composition .by. a continuousprocess.

In accordance with the essential features of the present invention. an.alkali cellulose -slurry is continuously formed by feeding, into aslurryforming :receptacle, cellulose 'and sodium hy- ,droxidesolutionwith a feeding rate maintained as uniform and constant as is practicablypossiblenbut always with the above mentioned unavoidable slightfluctuations in feeding'rate of the .cellulose. The -formed alkalicellulose slurryis continuously removed'at-aconstant volume rate by ametering gear pump or the like. The metered constant volume of slurryvremoved from the receptacle will, of course, contain' slight fluctuatingamounts of alkali cellulose corresponding to the slight fluctuations insaid feeding rate of cellulose. The fluctuations in alkali cellulosecontent of the slurry naturally will not exactly correspond to thefluctuations in feeding rate of cellulose since theslurry iscontinuously being formed in a receptacle of considerable size.

The slurry press rolls, when operating at a given peripheral speed, willpass alkali cellulose at a substantially constant volume of alkalicellulose regardless of the fluctuations of the alkali cellulose contentof the slurry being pressed. When a slightly thicker slurryis beingpassed into the slurry separating container, due to a slightly increasedfeeding rate of cellulose, the total volume of slurry being pressed perunit of time by the slurry press rolls will be decreased and thepressure will build up in the slurry separating container. It istherefore necessary to have a fluctuating volume receiver 38 between themetering device 34 and the slurry press rolls 42 and M. This receivermust be of such a size as to permit the increase and decrease of thetotal volume of slurry contained between the metering device and pressrolls to compensate for the maximum fluctuations which will occur in thefeeding rate ofthe cellulose and/or sodium hydroxide solution. As ageneral rule, the fluctuating volume receiver should have a ca pacity atleast equal to the total volume passed by the metering device in oneminute.

The constant level supply means for feeding sodium hydroxide to thereceptacle l may be a conventional float-controlled constant levelsupply device, or any other conventional means for feeding sufiicientsodium hydroxide solution to maintain constant the level of the slurryin the slurry-forming receptacle. Although much less desirable from apractical operating viewpoint, the sodium hydroxide may be supplied tothe receptacle ill at a constant metered rate, and such an apparatus isconsidered to be within the broad concept of the present invention.

Obviously, numerous other changes and modifications can be made in thedetails of the specifically illustrated and described apparatus withoutsubstantially departing from the nature and spirit of the invention. Forexample, although it is much to be desired, temperature control means,which is present for the purpose of avoiding changes in swellingcharacteristics of alkali cellulose, may, under certain conditions, bedispensed with. Similarly, the means for recirculating the slurry massfrom the receptacle by means of conduit 36 may be dispensed with, ifother means are provided to produce a uniform slurry mass in thereceptacle.

Although the invention has been described with particular reference tothe feeding of cellulose in sheet form, obviously, the cellulose may bein any other desired form, for example in the form of a continuous webor roll or even in the form of bulk pulp, wet. pulp, or a thickenedslurry obtained from a pulp mill.

In accordance with the present invention, alkali cellulose of uniformcomposition and containing a uniform percentage of residual sodiumhydroxide solution can be produced in a continuous manner despite thefact that it is practicably impossible to feed cellulose to aslurryforming receptacle in a constant rate per unit of time. Thepresent invention furthermore provides an apparatus which overcomes anumber of objections and limitations of previously known apparatus. Bythe practice of the present invention, it is possible to use celluloseof somewhat varying characteristics and it has been found possible touse a sodium hydroxide solution containing higher percentages ofhemicellulose than has been possible with processes known prior to thepresent'invention.

By means of the present invention, it is possible to increase ordecrease the average time of reacting the cellulose with the causticsoda solution, or increase or'decrease the viscosity of the slurry bymerely altering the rate of metering of the slurry to the press rolls,without any change in the rate of feed of the cellulose or the speed of.the press rolls. Since it is obvious that many changes andmodifications can be made in the details above described withoutdeparting from the nature and spirit of the invention, it is to beunderstood that the invention is not to be limited to the above detailsexcept as set forth in the appended claims.

We claim:

1. Apparatus for the production of a slurry of uniform compositioncomprising a receptacle; a device to maintain a constant level of liquidin said receptacle comprising an inlet to said receptacle and attachedto said inlet a container equipped with a supply conduit and an overflowconduit; an inlet in said receptacle for solids; agitators in saidreceptacle to form said slurry; in the lower portion of said receptaclean outlet for said slurry; a metering pump connected to said outlet; areceiver for said slurry connected to said metering pump and havingsufiicient volume for the level of said slurry to fluctuate freelytherein with pressure; a conduit in the lower portion of said receiverand connected to said conduit a slurry separating device comprising acontainer having rotatable press rolls sealed therein to maintain saidslurry under pressure and to pass said slurry out of said device.

2-. Apparatus for the production of a slurry of uniform compositioncomprising a receptacle; a device to maintain a constant level of liquidin said receptacle comprising an inlet to said receptacle and attachedto said inlet a container equipped with a supply conduit and an overflowconduit; a second inlet to said receptacle for solids; agitators in saidreceptacle to form said slurry; in the lower portion of said receptaclean outlet for said slurry; a metering pump connected to said outlet; areceiver for said slurry connected to said pump and having a capacity atleast equal to the total volume passed by said pump in one minute topermit the level of said slurry in said receiver to fluctuate freelytherein with pressure; a conduit in the lower portion of said receiverand connected to said conduit a slurry separating device comprising acontainer having rotatable press rolls sealed therein to maintain saidslurry under pressure and to pass said slurry out of said device.

3. Apparatus for the production of a slurry of uniform compositioncomprising a receptacle; a device to maintain a constant level of liquidin said receptacle; an inlet in said receptacle for solids; agitators insaid receptacle to form said slurry; in the lower portion of saidreceptacle an outlet for said slurry; a metering pump connected to saidoutlet; a receiver for said slurry connected to said metering pump andhaving sufncient volume dor. the level'of-said slurrytcafluctuate freelytherein with pressure; a conduit in the lower portion of" saidreceiverand connected tOZsaid conduit a slurryseparating devicecomprising-a container having'rotatable press rolls sealedtherein 'to'maintain said slurry under pressure and to pass said slurry out of saiddevice.

.4. Apparatus for the production of 2a slurry of uniformcompositionzcomprising a receptacle; a .device to maintain a constantlevel of liquid in said receptacle; a second inlet to said receptacle.for solids; agitators in said receptacle to form said slurry; in thelower, portion of said receptacle an outlet for said slurry; a meteringpump connectedto said outlet; areceiver for said slurry connected tosaid pumpand having a capacity at least equal to the total volume passedby said pump in one minute to permit the level of said slurry .sinasaidreceiver to fluctuatet freely therein 'with pressureya. conduit inithelower portion of said. receiveriandconnected to said conduit aslurry'separating'device comprising a container having rotatable; press.rolls sealed therein to imaintainvsaidslurry under pressure and. topass said slurry out of saiddevice.

WILLIAM .H. BRADSHAW. WILLIAM R. SCHMITZ, JR.

REFERENCES CITED .The followingreterences are of record in the file ofthis :patent:

1. APPARATUS FOR THE PRODUCTION OF A SLURRY OF UNIFORM COMPOSITIONCOMPRISING A RECEPTACLE; A DEVICE TO MAINTAIN A CONSTANT LEVEL OF LIQUIDIN SAID RECEPTACLE COMPRISING AN INLET TO SAID RECEPTACLE AND ATTACHEDTO SAID INLET A CONTAINER EQUIPPED WITH A SUPPLY CONDUIT AND AN OVERFLOWCONDUIT; AN INLET IN SAID RECEPTACLE FOR SOLIDS; AGITATORS IN SAIDRECEPTACLE TO FORM SAID SLURRY; IN THE LOWER PORTION OF SAID RECEPTACLEAN OUTLET FOR SAID SLURRY; A METERING PUMP CONNECTED TO SAID OUTLET; ARECEIVER FOR SAID SLURRY CONNECTED TO SAID METERING PUMP AND HAVINGSUFFICIENT VOLUME FOR THE LEVEL OF SAID SLURRY TO FLUCTUATE FREELYTHEREIN WITH PRESSURE; A CONDUIT IN THE LOWER PORTION OF SAID RECEIVERAND CONNECTED TO SAID CONDUIT A SLURRY SEPARATING DEVICE COMPRISING ACONTAINER HAVING ROTATABLE PRESS ROLLS SEALED THEREIN TO MAINTAIN SAIDSLURRY UNDER PRESSURE AND TO PASS SAID SLURRY OUT OF SAID DEVICE.